Coaxial resonators are used in oscillators, filters, duplex filters and other electronic circuits where a distributed inductance and capacitance is needed. Coaxial resonators can be made from ceramic materials or metal and can have a variety of shapes such, as square, rectangular, circular or cylindrical.
Coaxial resonators typically include one or more cylindrical passages, called through-holes, extending through a block or core of ceramic material. The block is substantially plated with a conductive material (i.e. metallized) on the outside walls and also on the inside walls formed by the resonator through-holes.
Coaxial resonators are typically either quarter wave resonators having one end fully metallized and the other end open (not metallized), or half wave resonators where both ends are open (not metallized).
The body of the coaxial resonator is typically soldered to a printed circuit board and a metal lead extends into the through-hole. The metal lead has one end soldered in the through-hole and the other end soldered to the printed circuit board. The use of metal leads creates unwanted parasitic effects in the circuit that can adversely affect some circuit designs.
A ceramic coaxial resonator can also be coupled to external circuitry such as a printed circuit board through the use of a consecutively plated pad on the outer conductor of the resonator that creates a capacitive coupling.
One problem with ceramic coaxial resonators is that different manufacturers use ceramic materials with slightly different dielectric constants, quality factor (Qu), and coupling methods that cause the coaxial resonators to have different shapes or footprints as mounted on the printed circuit board. This creates difficulty for other manufacturers to be able to exactly match the same shape or footprint that currently exists and therefore causes problems in adding additional suppliers of the coaxial resonators.
What is needed is a resonator coupling method that can match an existing coaxial resonator shape or footprint using a wide variety of ceramic materials that have different dielectric constants.